Avian Pollination:
Ecology of Vision and Colouration
in a Co-evolved System
Laila Gao
Avian colour vision differs substantially from that of humans because many birds
perceive UVA wavelengths (300-400nm), to which humans are blind, and have four
types of cones in their retina, compared to only three in humans. Thus, to
communicate with their pollinators, plants may use colour-based signals “hidden”
from humans. With the objective of gaining insight into the function and evolution of
colour-based signalling in avian pollination systems, we carried out a range of
observations and experiments in the coastal heathlands of Royal National Park,
Australia (figure 1).
Figure 1: Our field-sites
were located in Royal
National Park (New
South Wales, Australia),
where I joined my
supervisor, Isabel Nelson,
from the University of
Bristol
(UK),
for
research
on
avian
pollination between June
and September, 2005.
(photo: J. Rankin)
Our first aim was to investigate the pollination biology of the fuchsia heath Epacris
longiflora (figure 2a). Twice a month, observations of flower visits were undertaken
in plots of 50m² in 30-minute time-slots throughout the day. We found that while
some birds legitimately visited the flowers, feeding through the corolla mouth and
thus pollinating the plant, others robbed the nectar by tearing holes in the petals or
feeding through such holes torn by previous visitors, not pollinating the plants. We
recorded data which included the species of nectar-feeding bird visiting, the number
of flowers visited per plant either legitimately or by robbing, and the number of intact
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and robbed flowers per plant. Legitimate avian flower visitors included the Eastern
Spinebill and the New Holland honeyeater. Robbers also included the New Holland
honeyeater and Silvereyes.
Furthermore, to measure nectar rewards available from Epacris longiflora, we
measured plant and flower density and floral display size. Therefore, we counted the
number of plants in 25m2 plots, the number of flowers and buds per plant in these
plots, and the number of buds, intact, and robbed flowers on randomly selected plants.
We measured nectar rewards per plant by removing the nectar with a micropipette and
bagging flowers with polyorganza material for 24 hours (figure 2b) to obtain nectar
production rates. We also took morphometric measurements of these flowers.
In addition, we conducted the following experiment to determine whether nectarfeeding birds could discriminate rewarding flowers before probing these: from half
the flowers on a plant we first removed the nectar and then replaced it with twice the
amount nectar, while from the other half of the flowers we removed the nectar and
replaced it with its original amount, as a control for the manipulation. Video cameras
were set up to record which flower treatments birds visited, as well as the approach
direction of the bird relative to the plant and the sun.
Figure 2: a) flowers and buds of Epacris
longiflora. b) a bag of polyorganza material is
placed on the flower to determine nectar
production rates (photos: J. Rankin and I.Nelson)
2a
2b
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Our second aim was to search for patterns of phenotypic clustering within the
flowering plant community, and to determine whether two flower traits, namely
colour and morphology, are correlated with pollinator types. Therefore, insects and
birds were observed and caught to identify the pollen of which plants they carried
(figure 3). The pollen grains collected from the pollinators will be identified by
comparing them to a pollen database, which is to be constructed by collecting pollen
directly from flowering plants at the field site.
Figure 3: Bird observations were
carried out along transects, and
birds were caught with mist nets.
Pollen was then collected by
stroking their bill and head with
fuchsin gel, which stains the
pollen grains sticking to it. The
bird species were recorded and the
birds were banded.
Insects were caught directly after
observing them pollinate plants
along transects, they were
identified, and pollen was removed
from their body with fuchsin gel.
(photo: I. Nelson)
Further floral measurements have been undertaken on flowering plant species at the
field site, including colour measurements. These were carried out by spectrometry
over the UVA and human-visible ranges, which allows reflectances and light
environments to be accurately assessed. Moreover, we started to set up a database on
pollination systems in Australia, based on published and unpublished literature. Thus,
we hope to increase understanding of signalling in Australian pollination systems.
I would like to thank the Explorers Club and my supervisor Isabel Nelson for giving
me the opportunity to travel to Australia to undertake this project and attain many
invaluable skills. In addition to learning the methodologies we employed to carry out
our research, I gained much knowledge of experimental design and application. I
realised how much thorough and strenuous work goes into organising and undertaking
a research project based on fieldwork, but also how rewarding this can be (figure 4).
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Figure 4: Above all, taking part in this research
project has been fun! Royal National Park - with
its exceptionally beautiful scenery - has provided
many unforgettable experiences. I found out how
much I enjoyed being outdoors all day, working
in relative isolation, and observing the wildlife
around me.This included a great variety of birds,
some of which we caught for pollen removal and
subsequently released, echidnas and wallabies passing
through our field site, and whales migrating close to
the coast. (photos: I. Nelson)
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